The present invention relates to a spectacle lens for the correction of an eyesight deficiency of a spectacle wearer as well as to a spectacle lens family comprising a plurality of such spectacle lenses. Furthermore, the invention relates to a method for the manufacture of such a spectacle lens as well as for the manufacture of the spectacle lenses of the spectacle lens family.
A spectacle lens for the correction of an eyesight deficiency is characterized by a nominal prismatic power for the correction of an eyesight deficiency as well as by a nominal dioptric power for the correction of the eyesight deficiency, the nominal dioptric power comprising in particular a nominal spherical power for the correction of a spherical eyesight deficiency and a nominal astigmatic power for the correction of an astigmatic eyesight deficiency. To this end, the degree of a spherical cut and a cylindrical or/and toroidal cut of the lens as well as the orientation thereof must be defined. Moreover, in many cases such a spectacle lens also provides a multifocal property which compensates a deficient adaptation capacity of the eye when changing from the viewing of a far object to the viewing of a near object. For this purpose, the spectacle lens has a so-called far-vision reference point and a so-called near-vision reference point spaced apart therefrom, the line of sight of the wearer, when viewing the far-away object, passing through the spectacle lens in the area of the far-vision reference point and, when viewing a near object with the line of sight extending downwardly, passing through the spectacle lens in the area of the near-vision reference point. The mean dioptric power of the spectacle lens at the near-vision reference point differs from the mean dioptric power of the spectacle lens at the far-vision reference point by a predetermined value, the so-called xe2x80x9cadditionxe2x80x9d. A spectacle lens which is adapted to a specific wearer is thus characterized at least by the parameters: nominal dioptric power, optionally the orientation thereof and the desired addition.
The spherical and astigmatic powers are usually indicated in diopters which are usually rounded up or down to the nearest fourth of a diopter.
The term xe2x80x9cmean spherical powerxe2x80x9d as used herein is defined as the mean value of the first and second main cut, as it is, for example, described in DIN 58208, part 1-25.
Due to the multiplicity of the characterizing parameters to be at least employed and the individual differences thereof between different spectacle wearers, it is apparent that an automatic manufacture of spectacle lenses requires an extreme flexibility as far as the parameters are concerned which characterize the spectacle lens.
A spectacle lens for the correction of an eyesight deficiency of a spectacle wearer is known from EP 0857993 A2, said lens likewise exhibiting a multifocal property. In said conventional spectacle lens the lens surface facing away from the wearer""s eye is of spherical or rotational-symmetric aspherical design. A plurality of spectacle lenses for the correction of different eyesight deficiencies have this shape of the lens surface facing away from the eye in common so that at least this lens surface is easy to manufacture even in individualized mass production. The correction of the eyesight deficiency, i.e., the provision of a spherical or/and toroidal cut, as well as the multifocal property, are provided by the lens surface facing towards the wearer""s eye.
The known spectacle lens has been found to be disadvantageous in so far as the common manufacture of spectacle lenses of specific different combinations of eyesight deficiencies result in excessively thick spectacle lenses and the imaging quality of the spectacle lenses is in need of improvement.
In one aspect, the present invention relates to a spectacle lens which combines good imaging properties with the ability to mass produce spectacle lenses for the correction of different eyesight deficiencies. In another aspect the present invention relates to a spectacle lens family, the members of which compensate different eyesight deficiencies and, at the same time, can be produced in common in mass production while a comparatively good imaging quality is maintained.
In another aspect, the present invention relates to a method for the manufacture of such a spectacle lens and such a spectacle lens family.
According to a first aspect, the invention provides a spectacle lens for the correction of an eye deficiency of a spectacle wearer, which spectacle lens comprises a lens surface facing towards the eye of the spectacle wearer and a lens surface facing away from the eye of the spectacle wearer.
Preferably, the lens surface facing towards the eye functions directly to correct the eyesight deficiency and its shape is therefore merely defined by a sphere and/or a torus so that, as a result, a nominal dioptric power is produced to compensate the spectacle wearer""s eyesight deficiency.
Preferably, the function of the lens surface facing away from the eye comprises, on the one hand, the provision of a multifocal property and, on the other hand, the compensation of certain imaging alterations which are due to the interactions between the eyesight deficiency correction provided by the lens surface facing towards the eye and the multifocal property provided by the lens surface facing away from the eye and which furthermore result from the interaction between the multifocal property and the specific geometric position of the spectacle lens relative to the spectacle wearer. The alterations caused by the geometric position of the spectacle lens relative to the spectacle wearer include in particular the following parameters:
Distance between the two eyes of the spectacle wearer.
The multifocal property of the spectacle lens is perceived by the spectacle wearer as desired if, when viewing a far object, his sightline passes through the far-vision reference point and, accordingly, when viewing a near object, his sightline passes through the near-vision reference point of the spectacle. It has been found that this requirement is fulfilled better if the near-vision reference point is offset further inwards relative to the far-vision reference point for a spectacle wearer having a large eye distance than for a spectacle wearer having a small eye distance.
Distance between the eye of the spectacle wearer and the spectacle lens when worn by the spectacle wearer, i.e., in its position of use.
It has been found that the distance between the eye and the spectacle lens likewise influences the effect of the multifocal property on the spectacle wearer and, accordingly, a correcting design of the lens surface facing away from the eye can be provided to the effect that the spectacle wearer perceives the multifocal property as optimal as possible. In this respect, it is particularly favorable for this distance to be incorporated also in the correction of the interaction between the eyesight deficiency correction and the multifocal property, and, moreover, it is also favorable, in order to define the position of the far-vision reference point and the near-vision reference point relative to one another, to take both the eye distance and the distance between eye an spectacle lens into consideration.
Inclination of the spectacle lens relative to the spectacle wearer when his sightline passes, for example, through the far-vision reference point to a distant object.
The alteration of the interaction between the eyesight deficiency correction and the multifocal property caused by an alteration of the spectacle lens inclination can also be reduced with a known spectacle lens inclination.
Preferred distance between the eye of the spectacle wearer and an object to be viewed in the near zone.
In order for the wearer to perceive viewing as pleasant when changing from distant vision to near vision, the imaging properties of the spectacle lens can also be favorably influenced in that the preferred distance of the object in the near zone is incorporated by the spectacle lens or the eye of the spectacle wearer already as correction in the design of the lens surface facing away from the eye.
If the eyesight deficiency compensation also includes a nominal prismatic power of the spectacle lens, it is also advantageous to take an interaction between the nominal prismatic power and the multifocal property of the spectacle lens into consideration in designing the lens surface facing away from the eye in terms of compensation.
Thickness of the spectacle lens.
Depending on the diameter and design of the spectacle frame desired for the spectacle lens, different thicknesses of the spectacle lens are required. The thickness of the lens may, for example, be defined at the far-vision reference point or at the center of the lens. In this respect, it is likewise favorable to take the thickness into consideration as far as the above-mentioned alterations are concerned.
In the spectacle lens according to the present invention one of the two lens surfaces thus has a surface shape which is merely composed of a sphere and a torus. Such a surface shape is comparatively easy to prepare in mass production in which, however, each spectacle lens can be prepared with different spheres or tori by grinding using appropriately designed grinding tools. The lens surface facing away from the eye has a more complicated shape, because, on the one hand, it provides a multifocal property and, on the other hand, the above-described compensation of the interaction between the eyesight deficiency correction and the multifocal property and an optimization in respect of the positioning of the spectacle lens relative to the spectacle wearer.
The spectacle lens is particularly suitable for an automatic mass production in which each spectacle lens produced can be produced with an individual design of the lens surface facing towards the eye for the correction of different eyesight deficiencies of a multiplicity of spectacle wearers.
Accordingly, a second aspect of the present invention relates to the provision of a spectacle lens family comprising a plurality of spectacle lenses which are particularly suitable for individual mass production. The spectacle lens family of the invention is based on a common design of the multifocal property. On the basis of a given near-vision reference point and a given far-vision reference point as well as the difference in the mean dioptric powers at the near-vision and far-vision reference points (xe2x80x9cadditionxe2x80x9d), said design comprises a specific distribution of astigmatic and spherical aberrations in the field of view of the spectacle wearer. This distribution of the spherical and astigmatic aberrations can characterize the spectacle lens family due to the multifocal property and distinguishes the same from other spectacle lens families. On the other hand, individual members of the spectacle lens family differ from one another in respect of the eyesight deficiency correction, i.e., in the nominal dioptric power or/and the nominal prismatic power, while exhibiting substantially the same or similar multifocal properties. Such spectacle lenses are particularly suitable for being produced in common as a spectacle lens family.
There are pairs of individual members of the spectacle lens family differing in respect of their nominal spherical or/and astigmatic power by less than 1 diopter, in particularly by less than 0.5 diopters, and in particular by 0.25 diopters.
1 diopter, 0.5 diopters and 0.25 diopters, respectively, are thus a xe2x80x9cdioptric pitchxe2x80x9d with which the spectacle lenses of the spectacle lens family are offered as far as the nominal spherical and astigmatic powers are concerned.
Although the function of the eyesight deficiency correction is a result of the shape of the lens surface facing towards the eye, and the multifocal properties of the members of the spectacle lens family are substantially the same or similar and provided by the lens surfaces facing away from the eye, the lens surfaces of the spectacle lenses facing away from the eye are nevertheless different in shape. This is due to the fact that the design of the multifocal property results into a basic shape of the lens surface facing away from the eye. However, this basic shape is then modified to take account of the effect of the different nominal spherical, astigmatic and prismatic powers, respectively, on the multifocal property and to influence the same such that the effect of the multifocal properties of the spectacle lens family on the wearer is substantially the same or similar.
The modification of the basic shape of the lens surface facing away from the eye advantageously comprises also the parameters mentioned above: eye distance of the spectacle wearer or/and distance between the eye and the spectacle lens or/and inclination of the spectacle lens relative to a sightline or/and preferred distance between the object viewed in the near zone and the eye or spectacle lens or/and a nominal prismatic power of the spectacle lens for the correction of a further eyesight deficiency or/and thickness of the spectacle lens.